A New Theory about the Earth’s Water is Here

November 21, 2018

Asteroids are not the only contributor to Earth’s water, a recent study suggests.

The source of all the water that we use every day has always been a mystery for the scientists and a number of hypotheses have been made in this regard from time to time. Recently, researchers from the American Geophysical Union proposed a new theory about the origin of Earth’s water that might just solve this long-lasting mystery. According to the study published in the journal ‘Journal of Geophysical Research: Planets’, both asteroidal material and gas left over from the formation of the Sun contributed to the Earth’s water. Traditionally, quite a lot of scientists believed that all of the water that we have on Earth came from asteroids.

The similarities between the water on asteroids and the ocean water was used as an evidence for supporting this idea. The ratio of Deuterium to Hydrogen is a vital chemical signature of water sources and prior studies showed that the deuterium-to-hydrogen ratio of Earth’s water is quite close to the water on asteroids. In contrast to that, researchers of the latest study suggested that some of the Hydrogen for Earth’s water came from the clouds of dust and gas remaining after the formation of the sun as the information from ocean water is incomplete. Steven Desch, a Co-author of the study who is a Professor of Astrophysics in the School of Earth and Space Exploration at the Arizona State University, referred to that by saying,

“It’s a bit of a blind spot in the community. When people measure the [deuterium-to-hydrogen] ratio in ocean water and they see that it is pretty close to what we see in asteroids, it was always easy to believe it all came from asteroids.”

The researching team led by Peter Buseck, a Regents’ Professor in the School of Molecular Sciences at the Arizona State University, further explained that the Hydrogen in ocean water doesn’t represent the Hydrogen throughout the planet. They analyzed some samples of Hydrogen from deep inside the Earth and found a significant drop in the quantity of Deuterium. This is a clear indication that this Hydrogen didn’t come from asteroids as they are quite rich in Deuterium. In addition to that, the presence of different isotopes of Helium and Neon, inherited from the solar nebula, were also found in these samples. They created a new theoretical model for Earth’s formation to explain the difference between Hydrogen at the core-mantle boundary of Earth and its oceans.

The paper explains that billions of years ago, large, waterlogged asteroids started to turn into planets while solar nebula was still circling around the sun. These asteroids, called Planetary Embryos, grew rapidly by colliding with each other. This ultimately resulted in a massive collision which melted the surface of the largest embryo into an ocean of magma. It eventually turned into a planet known as Earth. The early atmosphere of this magma-covered embryo was made from the Noble Gases and Hydrogen, which were drawn from the solar nebula. At that time, Nebular Hydrogen dissolved into the molten iron of the magma ocean. Hydrogen was later pulled towards the center of the young Earth by a process called Isotopic Fractionation.

It delivered most of the Hydrogen to the core due to its attraction towards Iron. On the other hand, Deuterium stayed in the magma and formed the mantle of the planet upon cooling. Asteroid strikes and impacts from smaller embryos continued to add water and mass to the planetary embryo until it reached its current size. This new model acknowledged that most of the water on Earth came from asteroids but solar nebula also made a substantial contribution to the cause. Jun Wu, an Assistant Research Professor in the School of Molecular Sciences and School of Earth and Space Exploration at Arizona State University who is also the Lead Author of the study, elaborated that by saying,

“For every 100 molecules of Earth’s water, there are one or two coming from solar nebula.”

This research might also help those scientists that are trying to study the development of other planets and their potential to support life. The authors suggested that a lot of Earth-like planets in other solar systems, who didn’t have access to waterlogged asteroids, could have obtained water through their solar nebula. Wu talked about that and said,

“This model suggests that the inevitable formation of water would likely occur on any sufficiently large rocky exoplanets in extrasolar systems. I think this is very exciting.”

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